The disclosure of Japanese Patent Application No. 12-149558 filed on May 22, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a sensing device for detecting a physical quantity such as angular speed, acceleration, pressure, etc., in accordance with the displacement of a vibrator spaced upwards from a substrate. The invention further relates to a sensor apparatus including the sensing device.
2. Description of Related Art
It is well known to provide a sensing device that has a vibrator displaceably supported on a substrate, a plurality of electrodes, each of which is composed of a movable electrode and a fixed electrode, and a plurality of wirings allowing passage of electric signals and that detects a physical quantity such as angular speed, and a sensor apparatus including such a sensing device. The movable electrode is connected to the vibrator and is displaced together therewith on the substrate. The fixed electrode is fixed onto the substrate in such a manner as to face the movable electrode. In this kind of sensing device, as disclosed for example in Japanese Patent Application Laid-Open No. 10-300475, compensating wirings are additionally provided on the substrate for the purpose of eliminating the influence of the parasitic capacitance of the above-described wirings, thus attaining an electrically suitable balance among the wirings.
However, in the sensing device and the sensor apparatus according to the above-mentioned related art the electrical characteristic of each of the wirings is not taken into consideration. That is, resistance, capacitance, and so on of each wiring is different because of the influence of errors (disperse) in length, width, thickness and so on of the wirings. Therefore, if a plurality of electrodes are used for driving purposes, driving forces of the electrodes disperse. Further, if a plurality of electrodes are used for detecting purposes, detection values obtained from the electrodes disperse. This will eventually lead to a problem of deterioration in detecting precision of the sensing device.
Further, in the sensing device of the above-described related art, problems associated with the manufacture of beams for supporting the vibrator with respect to the substrate are not taken into account. The beams may develop notches during the manufacture. Development of notches makes vibrations of the vibrator uneven and unstable and eventually causes deterioration in detecting precision of the sensing device.
The invention is a solution to the above-mentioned problems. It is an object of the invention to provide a sensing device and a sensor apparatus capable of precise detection.
In order to achieve the above-stated object, the invention provides a sensing device comprising a vibrator displaceably supported on a substrate, a plurality of electrodes each of which comprises a movable electrode that is connected to the vibrator and that is displaced together with the vibrator on the substrate and a fixed electrode that is fixed onto the substrate in such a manner as to face the movable electrode, and a plurality of conductors (or wirings) provided on the substrate and connected to the movable and fixed electrodes to allow passage of electric signals, wherein one electrical characteristic is set for those of the conductors which allow passage of electric signals of the same kind. In this case, it is appropriate that one electrical characteristic is set for those of the conductors by equalizing length, width, and thickness of those of conductors which allow passage of electric signals of the same kind.
In this construction, one electrical characteristic is set for those of the conductors which allow passage of electric signals of the same kind. Therefore, if a plurality of electrodes are used for driving purposes, driving voltages applied to the electrodes become equal to one another, thus reducing dispersion of driving forces. Further, if a plurality of electrodes are used for detecting purposes, dispersion in detecting voltages of the electrodes is reduced. As a result, the detecting precision of the sensing device is improved.
A plurality of beams are provided between the substrate and the vibrator to displace the vibrator, the distance between one of the beams and another beam or member that is close to one side of the one of the beams and that extends parallel thereto is set equal to the distance between the one of the beams and still another beam or member that is close to the other side of the one of the beams and that extends parallel thereto.
In this construction, opposed sides of each of the beams are formed symmetrically when the conductors are formed by etching. For instance, even if notches have developed on opposed sides of each of the beams due to etching, the notches are formed symmetrically. Therefore, dispersion in electrical characteristics of the conductors can be easily reduced and thus one electrical characteristic can be easily set for a plurality of conductors.